This investigation is concerned with the mechanisms that control blood flow in the cochlea, the degree or magnitude of such control, and the physical locations of the effectors of the control. The nature of the blood-perilymph and blood-endolymp barriers are of additional interest as is the influence of the sympathetic nervous system on the cochlear blood supply. In-vivo blood flow velocity and blood vessel diameters are to be measured in several regions of the cochlea (modiolus, stria vascularis, spiral ligament, osseous sprial lamina, and basilar membrane) using light microscopic techniques. Analog and digital techniques will allow quantification of flow and vessel diameter changes for altered systemic blood pressure, cervical sympathetic ganglion electric stimulation, CO2 respiration, vasoactive drugs, and intense sound. Extensive use will be made of fluorescence techniques using fluorescein isothiocyanate labeled dextran and dichlorazinylaminofluorescein labeled red blood cells. Other fluorchomes including rhodamine and acridine red are also to be used. The dyes will be excited by xenon light epi-illumination or transillumination and recorded by an image intensified video camera and recording system. The digital analysis of cochlear vasculature will make use of digital image processing techniques to enhance the pictures. Oxygen sensitive microelectrides and pH sensitive microelectrodes will be used to measure intracochlear PO2 and pH values. Cochlear microphonics and compound action potentials in response to acoustic stimuli will also be determined. Regional blood flow in the cochlea will also be measured using a hydrogen clearance method. The ultimate goal is to determine the factors that influence inner ear microcirculation and the effect that these have on the inner ear. The studies should help clarify the role that mocrocirculation has in sudden deafness, fluctant hearing, sound induced hearing loss, and Meniere's disease.